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Bacteria

Many of us know bacteria only as “germs,” invisible creatures that can invade our bodies and make us sick.

Few know that many bacteria not only coexist with us all the time, but help us do an amazing array of useful things like make vitamins, break down some garbage, and even maintain our atmosphere.

Bacteria consist of only a single cell, but don't let their small size and seeming simplicity fool you. They're an amazingly complex and fascinating group of creatures. Bacteria have been found that can live in temperatures above the boiling point and in cold that would freeze your blood. They "eat" everything from sugar and starch to sunlight, sulfur and iron. There's even a species of bacteria—Deinococcus radiodurans—that can withstand blasts of radiation 1,000 times greater than would kill a human being.

Classification

Bacteria fall into a category of life called the Prokaryotes (pro-carry-oats). Prokaryotes' genetic material, or DNA, is not enclosed in a cellular compartment called the nucleus.

Bacteria and archaea are the only prokaryotes. All other life forms are Eukaryotes (you-carry-oats), creatures whose cells have nuclei.

(Note: viruses are not considered true cells, so they don't fit into either of these categories.)

What Difference Does It Make?

Does a bacterium’s cell wall, shape, way of moving, and environment really matter?

Yes! The more we know about bacteria, the more we are able to figure out how to make microbes work for us or stop dangerous ones from causing serious harm. And, for those of us who like to ponder more philosophical questions like the origins of the Earth, there may be some clues there as well.

How Long They’ve Been Around

Like dinosaurs, bacteria left behind fossils. The big difference is that it takes a microscope to see them. And they are older.

Bacteria and their microbial cousins the archaea were the earliest forms of life on Earth. And may have played a role in shaping our planet into one that could support the larger life forms we know today by developing photosynthesis.

Cyanobacteria fossils date back more than 3 billion years. These photosynthetic bacteria paved the way for today's algae and plants. Cyanobacteria grow in the water, where they produce much of the oxygen that we breathe. Once considered a form of algae, they are also known as blue-green algae.

Bacteria are among the earliest forms of life that appeared on Earth billions of years ago. Scientists think that they helped shape and change the young planet's environment, eventually creating atmospheric oxygen that enabled other, more complex life forms to develop. Many believe that more complex cells developed as once free-living bacteria took up residence in other cells, eventually becoming the organelles in modern complex cells. The mitochondria (mite-oh-con-dree-uh) that make energy for your body cells is one example of such an organelle.

Some bacteria are photosynthetic (foe-toe-sin-theh-tick)—they can make their own food from sunlight, just like plants. Also like plants, they give off oxygen. Other bacteria absorb food from the material they live on or in. Some of these bacteria can live off unusual "foods" such as iron or sulfur. The microbes that live in your gut absorb nutrients from the digested food you've eaten.

Some bacteria have hair- or whip-like appendages called flagella used to ‘swim’ around. Others produce thick coats of slime and ‘glide’ about. Some stick out thin, rigid spikes called fimbriae to help hold them to surfaces. Some contain little particles of minerals that orient with the planet’s magnetic fields to help the bacteria figure out whether they’re swimming up or down.

Bacteria can be found virtually everywhere. They are in the air, the soil, and water, and in and on plants and animals, including us. A single teaspoon of topsoil contains about a billion bacterial cells (and about 120,000 fungal cells and some 25,000 algal cells). The human mouth is home to more than 500 species of bacteria.

Some bacteria (along with archaea) thrive in the most forbidding, uninviting places on Earth, from nearly-boiling hot springs to super-chilled Antarctic lakes buried under sheets of ice. Microbes that dwell in these extreme habitats are aptly called extremophiles.

Archaeans are among the earliest forms of life that appeared on Earth billions of years ago. It’s now generally believed that the archaea and bacteria developed separately from a common ancestor nearly 4 billion years ago. Millions of years later, the ancestors of today's eukaryotes split off from the archaea. So historically, archaeans are more closely related to us than they are to bacteria.

Does a bacterium’s cell wall, shape, way of moving, and environment really matter?

Yes! The more we know about bacteria, the more we are able to figure out how to make microbes work for us or stop dangerous ones from causing serious harm. And, for those of us who like to ponder more philosophical questions like the origins of the Earth, there may be some clues there as well.